1. Field of the Invention
The present invention relates to hydraulic valves, and in particular to valve assemblies having a plurality of sections butted together to control several functions of a machine.
2. Description of the Related Art
Construction and agricultural machines employ a hydraulic system to operate different mechanical devices. For example a backhoe is a common earth moving machine that has a bucket attached to the end of an arm which in turn is coupled by a boom to a tractor. Separate hydraulic cylinders are connected between adjacent ones of those elements to produce movement of one with respect to the other, which operation is commonly referred to as a “function” of the machine. The machine operator controls a given function by operating a valve that governs the flow of pressurized fluid from a pump to the associated cylinder and back to a tank. Hydraulic motors and other types of actuators also are used to move machine elements.
Each valve is part of an assembly that controls the operation of several machine functions. In the case of a backhoe, an assembly of four valves may be provided in the assembly to swivel and tilt the boom, move the arm, and tilt the bucket. U.S. Pat. No. 4,693,272 describes a typical valve assembly having a plurality of individual sections butted side by side, with each section containing one of the control valves and associated components. Each valve section has a bore in which a control spool slides to meter fluid between a pair of workports and the supply and tank return lines.
The valve sections have through passages for the supply line, tank return line, and load sense circuit. When a plurality of these sections are butted side by side these passages align to convey fluid through the entire assembly. It is common in prior designs, the through passages intersect the spool bore so that the fluid flows around the control spool from one section to another. The high pressure and pressure changes in these fluid passages as compared to other regions of the valve section commonly produced physical distortion of the spool bore. Another common feature that contributed to bore distortion was a bridge galley used in the valve section to convey pressurized fluid between portions of the spool bore.
The valve sections are bolted between end sections that have ports to connect the supply and tank hoses to the assembly. Heretofore a relatively large contact area was machined on opposite side walls of each valve section to provide surfaces against which the adjacent assembly sections abutted. The through passages had openings in those surfaces which aligned with similar openings in the abutting section. Unless the large contact area was machined extremely flat and parallel to the area on the opposite side surface, proper contact with the abutting section was not achieved and the assembly fastening force distorted the valve section and its spool bore.
Therefore it is desirable to design a valve section in which the effects of these distortion producing characteristics are minimized.